The long tail of Steam (PC) games aren't really made for small screens and controllers. For a game to be "verified", it needs to fully support controllers, have readable text on a 8" 1280x800 screen and run well on Deck's hardware using Proton.

As more older Steam games went through the process, less % of games actually fulfill those conditions (main reason I'm personally seeing is either "small text" or a launcher that requires use of mouse to click "Play" before the game starts).

They probably have put the most effort into making popular games work, but as time as gone one, they've tried to “verify” more and more less popular games. I'm assuming here that there is a missing “not previously reviewed” segment in the graph, i.e. there are less games at the start than at the end.

There's a finite amount of validation effort available and presumably in the early days there was a focus on highlighting the games that best demonstrated the Deck's selling points. It stands to reason that as time goes by and the low hanging fruit has been picked, validation effort instead goes into more and more obscure or less obviously Deck friendly games.

Because the ratio of verified was too optimistic in the beginning - and potentially the current ratio is closer to the reality, with a minority of games released on PC actually made to work well on a smaller screen.

Note that requiring a launcher, or keyboard input also make the games land in playable territory even though it works perfectly otherwise.

1. Hardware requirements increase with time while the platform being verified against remains the same. They may run... just not well due to hardware limitations

2. Varies depending on how many games implement incompatible things like certain anti-cheats. Admittedly, this may only account for a small amount. They come/go in waves -- eg: looter/shooter trend

3. Steam Deck verified is a more strict qualification than Linux in general; tiny screen/resolution, gamepads, etc.

4. Finally, inconsistency between the rate-of-verification and rate-of-addition - these are not locked

Probably more, these are what immediately come to mind

My theories: (1) Steam got a lot of new games. (2) Compatibility issues found deep inside games. (3) No compat issues, but issues with Steam Deck specifically.

considering the amount of new games each day on steam, it doesn't surprise me